Dehydration in the elderly has significant morbidity and mortality. Salivary glands require body fluids for normal function, and saliva is essential for the maintenance of oral health. It is currently accepted that salivary gland function is age-stable in healthy adults. It is also believed that systemic diseases and their treatment (e.g. medications, head and neck radiation) alter salivary function and account for the high prevalence of salivary gland dysfunction and complaints of dry mouth (xerostomia) in older populations. However, there is little information concerning the relationship between body hydration and salivary gland output. The aims of this study, therefore, are: 1) to determine if there is a relationship between unstimulated and stimulated parotid salivary gland flow rates and hydration levels in healthy individuals, and 2) to determine if the relationship between parotid salivary gland flow rates and hydration is dependent upon age. The hypotheses of this study are: 1) there will be an increase in unstimulated and stimulated parotid flow rates in a hydrated versus a non-hydrated group, and 2) the increase in parotid flow rates due to hydration will be independent of age. The research design will involve 30 young (age 20-40 years) and 30 old (age 60-80 years) healthy and unmedicated males and females. Subjects will be recruited from the Human Subjects Core of the University of Michigan Geriatrics Center, and will be examined in the General Clinical Research Center at the University of Michigan Hospital. Following a 12 hour overnight fast and review of informed consent, subjects will be weighed, complete a brief xerostomia questionnaire, have unstimulated and 2% citrate-stimulated parotid saliva collected, have an IV started in one arm, and have several blood samples collected. Half of the young and half of the old study subjects will be randomly assigned to receive hydration via an IV (15 ml/kg of isotonic saline for one hour), and the remaining half will not receive any hydration. Following the hydration/non-hydration period the xerostomia questionnaire will be repeated, and unstimulated and 2% citrate-stimulated parotid saliva and blood samples collected. The questionnaire, saliva and blood samples will also be collected one hour following the hydration/non-hydration period. Blood pressures and pulse rates will be measured every 15 minutes, and each subject's EKG will be monitored for significant changes during the course of the study to minimize any potential risks. The purpose of the xerostomia questionnaire is to determine if there is a relationship between subjective feelings of mouth dryness with changes in hydration. Blood samples will be analyzed for serum sodium, total proteins, hematocrit, blood urea nitrogen, creatinine, and aldosterone in order to establish a hydration level for each participant before, during, and after the hydration/non-hydration period and as accurate estimates of osmoregulation. Serum aldosterone is a sensitive marker of hydration status, and is believed to have similar effects on salivary glands as renal tubules. Results from this study can help determine the relationship between hydration and salivary function and will substantiate further research on oral health and dehydration. Older adults are the most rapidly growing segment of the population, and dehydration and dry mouth are significant problems among the elderly. Results from this study can also determine if the salivary response to hydration in older adults is similar to that among young people. This data will hopefully assist in the identification of populations at risk for salivary gland dysfunction.